The present invention relates to metal joints and, more particularly, to improved means and method for soldering return bend connectors to heat exchange tubes of heat exchangers wherein at least one of the members is aluminum.
A joint between tubular members of a heat exchange must provide a freon tight seal to assure the integrity of the heat exchanger system. The soldering of such joints, particularly where one or both of the tubular members is aluminum, presents certain problems such as difficulties resulting from a tenacious oxide coating that normally forms on aluminum and prevents the making of a good soldered joint, as well as the need for complex and expensive tooling in order to provide great dimensional accuracy and proper alignment of members to be joined because solder employed in forming aluminum joints does not flow readily into small spaces. While it is desirable to employ relatively large clearances in the joint to facilitate the flow of solder, it has been found that there is a maximum clearance as well as a minimum clearance that should be controlled.
Prior attempts at joining multi-row aluminum return bend connectors to heat exchanger tubes by the application of ultra-sonic energy to the solder bath during a dip soldering operation have achieved a certain degree of success but have not provided a satisfactory solution to other problems including the proper alignment of the members to be joined, the provision of means securing the members together to prevent their separation when they are inverted during a dip soldering operation, and the provision of proper venting of hot gases generated during the soldering operation.
In accordance with the present invention, longitudinal grooves are formed along the outer surface of a first tubular element and the metal displaced in forming the grooves forms projections or nibs depending outwardly from said surface a predetermined distance for an interference fit when said element is assembled telescopically in a solder cup formed in another tubular element. The frictional engagement resulting from the interference fit prevents separation of the elements when they are inverted and insures proper alignment thereof, and the grooves provide vent passageways for hot gases generated during a soldering operation.